Evaluating Interim Progression: First Posttherapy ¹⁷⁷Lu-PSMA SPECT/CT Relative to Baseline PSMA PET/CT

Area of Science:

• Oncology
• Nuclear Medicine
• Radiopharmaceutical Therapy

Background:

• Prostate-Specific Membrane Antigen (PSMA) PET is recommended for assessing treatment response in advanced prostate cancer.
• The timing of PSMA PET relative to therapy initiation is crucial for accurate response assessment.
• Interim disease progression can impact the reliability of PET scans as a response evaluation tool.

Purpose of the Study:

• To evaluate the frequency of interim disease progression on post-therapy SPECT/CT.
• To determine the impact of the time interval between baseline PSMA PET and therapy initiation on interim progression.
• To compare outcomes between patients with and without interim progression.

Main Methods:

• Visual assessment of interim disease progression on first post-therapy ¹⁷⁷Lu-PSMA-617 SPECT/CT in 87 patients.
• Comparison of time intervals, pretherapy PSA, and treatment outcomes.
• Statistical analysis adjusting for age, Gleason grade, and PSA doubling time.

Main Results:

• 36.8% of patients showed interim progression.
• A longer PET-to-therapy interval (88 days vs. 42 days) was significantly associated with interim progression (P < 0.001).
• Approximately 94% of patients with interim progression had a PET-to-therapy interval exceeding 30 days.

Conclusions:

• A baseline PSMA PET may not accurately reflect disease status if therapy initiation is delayed by more than 30 days.
• Interim progression did not significantly impact PSA response or overall survival in this cohort.
• Optimizing the timing between PSMA PET imaging and ¹⁷⁷Lu-PSMA-617 therapy is essential for reliable response assessment.